Knitted socks of the “invisible” or “secret” type are widely used and appreciated. They have no leg portion, and extend below the ankle, so that, in use, they do not emerge from the footwear, but remain “concealed” within the footwear.
A problem that is frequently encountered in the use of these invisible socks is the tendency of their rear part to fall down and bunch up in a rather troublesome way under the sole of the user's foot.
To overcome this problem, WO2008/006525A1 proposes the application of at least one localized protruding element of adhesive polymer material, particularly an elastomeric material (such as silicone), to the inner surface of the rear part or heel of these socks, this material being adapted to increase the friction between the sock and the foot.
This solution, based primarily on the creation of a non-slip effect, cannot be implemented directly in knitting machines used for manufacturing socks.
The application of the aforesaid non-slip elements is carried out subsequently, and, when executed in a “mechanized” way, represents a complication of the production process, requiring additional processing that has a significant effect on the final cost of the products.
Moreover, the aforesaid non-slip elements may also be uncomfortable. They also fail to increase the friction between the sock and the footwear.
Another known solution, which is an alternative to the non-slip elements described above, provides for the insertion into various different parts of an invisible sock of threads or yarns made of elastomeric materials, covered if necessary (for example, polyamide-covered “elastane”, or nylon-covered Lycra™), which are capable of providing an elastic compressive action in order to improve the adhesion of the sock to the foot by impeding the slipping of the sock.